The Mouse Core is designed to establish the transgenic mouse lines required by the PPG investigators. It is also responsible for the crossing of these various lines with mice deficient in various genes as a result of targeted mutations. The Core will also be responsible for all breeding and genotyping required for supplying the animals described in this proposal. Specifically, the Mouse Core will be responsible for the following: 1. Identification of founder animals after pronuclear injection of mouse embryos with the following constructs: CCSP-hP2U-R; CCSP-(beta, gamma) rENaC; CCSP-tri-cistronic (alpha, beta, gamma) rENac; CSSP(alpha, beta/T, gamma) rENaC. Breeding of the above founders in order to establish lines homozygous for each of the transgenes. Breeding sufficient numbers for the experiments outlined in the projects described in this application. 2. Breeding sufficient numbers of mice carrying mutations introduced by homologous recombination into the P2U-R, and ENaC loci for the experiments described. 3. Breeding to obtain mice with the following combination of mutations: (1) breeding for mice carrying transgenes for all sub-units (alpha, beta, gamma) of the sodium channel e.g., breeding CCSP-alpha rENaC animals with CCSP-(beta, gamma) rENac animals, CCSP (alpha, beta, gamma) rENaC; (2) breeding of these animals with CFTR(-/-) animals to obtain animals which overexpress the Na channel and do not express the CFTR gene; (3) breeding of P2U-R(-/-) animals with CFTR(-/-). 4. Introducing transgene mutations onto an inbred mouse stain. 5. Providing pregnant animals for projects.